The structural analysis of a substance can be performed in such a manner that pigments or the like are fixed to the substance (e.g., protein), the substance is then excited by light, and the spectrum of fluorescence emitted from the substance is observed to evaluate the structure or behavior of the substance. Moreover, when rare-earth elements or the like are mixed with various base materials such as plastic and inorganic materials, fluorescence is observed by excitation of the base materials with light. Any change in a base material also changes the observed fluorescence spectrum. Therefore, the structure or the like of a base material can be analyzed by analyzing the fluorescence spectrum.
For the evaluation of a fluorescence spectrum, a measuring substance is irradiated and excited generally using a halogen lamp or the like. The fluorescence observed is evaluated with a spectroscope. FIG. 6 shows the configuration of the spectroscope.
Fluorescence 42 from a measuring substance 40 that has been irradiated with excitation light 41 is converged to a slit 44 by a lens 43. The fluorescence passing through the slit 44 is collimated by a lens 45 and then is directed to a diffraction grating 46. Light 48 that is diffracted by the diffraction grating 46 and passes through a slit 47 is observed, and a fluorescence spectrum is determined in accordance with the intensity distribution of the light 48.
There is another method for analyzing a fluorescence spectrum obtained by excitation with an Ar gas laser or semiconductor laser. When fluorescence from a living body is observed by irradiating it with a red semiconductor laser having a wavelength of 660 nm, a narrow-band-pass filter is used to separate the fluorescence from the excitation light because the fluorescence peak is 670 nm (e.g., Japanese Patent No. 3291898).
In the conventional configuration, a semiconductor layer, a gas laser, or the like is used as an excitation laser for exciting a substance, and the intensity of fluorescence generated from the substance is evaluated. However, such detection has disadvantages in that, e.g., when a plastic material contains rare earth, a slight structural change of the plastic material cannot be observed precisely.
In a detection system, the resultant fluorescence spectrum is diffracted by a reflection-type grating, and then is observed and detected by a CCD camera or the like. The use of a reflection-type grating in a spectral system increases the size of the device and causes a problem of stability. Moreover, the detection system including a CCD camera is expensive, and a long detection time is required to analyze the resultant fluorescence spectrum.